The present invention relates to mutant xcex1-amylases having improved productivity.
xcex1-Amylases [EC.3.2.1.1.] have been used in a wide range of industrial fields such as starch industry, brewing industry, fiber industry, pharmaceutical industry and food industry. Among them, those capable of degrading starches at high random are suited for detergents. Conventionally known as such are, as well as xcex1-amylases derived from Bacillus licheniformis, liquefying alkaline xcex1-amylases derived from the alkaliphilic strain Bacillus sp. KSM-AP1378 (FERM BP-3048) (WO94/26881) and improved enzymes having improved heat resistance and oxidant resistance (WO98/44126).
The present inventors have recently found liquefying alkaline xcex1-amylases derived from the alkaliphilic strain Bacillus sp. KSM-K38 (FERM BP-6946) and having chelating-agent- and oxidation-resistance (Japanese Patent Application No. Hei 10-362487, Japanese Patent Application No. Hei 10-362488); and improved enzymes having improved heat resistance (Japanese Patent Application No. Hei 11-163569).
In addition to such properties, enzymes for detergents are required to have high productivity in consideration of their industrial production. Although various trials have been made to improve the heat resistance or oxidant resistance of xcex1-amylases for detergent by using protein engineering technique, neither improvement of productivity has been considered sufficiently nor an attempt of production increase by mutation of a structural gene has been reported yet.
An object of the present invention is to provide mutant xcex1-amylases having excellent productivity.
The present inventors introduced, in microorganisms, mutant xcex1-amylase structural gene constructed by site-directed mutagenesis and evaluated productivity of xcex1-amylases. As a result, it has been found that since an xcex1-amylase gene has a site taking part in the improvement of productivity, introduction, into a microorganism, of a recombinant gene having this site mutated makes it possible to produce xcex1-amylases having drastically improved productivity.
In one aspect of the present invention, there is thus provided a mutant xcex1-amylase which is derived from an xcex1-amylase having an amino acid sequence represented by SEQ ED No. 2 or showing at least 60% homology thereto by substitution or deletion of at least one amino acid residue corresponding to any one of Pro18, Gln86, Glu130, Asn154, Arg171, Ala186, Glu212, Val222, Tyr243) Pro260, Lys269, Glu276, Asn277, Arg310, Glu360, Gln391, Trp439, Lys444, Asn471 and Gly476 of the amino acid sequence.
In another aspect of the present invention, there is also provided a mutant xcex1-amylase derived from an xcex1-amylase having an amino acid sequence represented by SEQ ID No. 4 or showing at least 60% homology thereto by substitution or deletion of at least one amino acid residue corresponding to any one of Asp128, Gly140, Ser144, Arg168, Asn181, Glu207, Phe272, Ser375, Trp434 and Glu466 of the amino acid sequence.
In a further aspect of the present invention, there is also provided a gene encoding this mutant xcex1-amylase, a vector containing the gene, a cell transformed with the vector and a production method of a mutant xcex1-amylase which comprises cultivating the transformed cell.
In a still further aspect of the present invention, there is also provided a detergent composition containing this mutant xcex1-amylase.